钠电池电解液添加剂的作用是什么？

What are the functions of additives in electrolytes for sodium-ion batteries?

电解液添加剂具备五大核心优化功能，全方位提升钠电池综合电化学与安全性能。第一界面改性，成膜添加剂优先在正负极界面发生氧化还原反应，生成薄而均匀的 SEI、CEI 钝化膜，减少电解液持续不可逆消耗，降低容量衰减速度，有效拉长循环使用年限；第二高低温性能优化，低温添加剂降低电解液整体粘度与凝固点，-20℃环境下大幅提升放电容量，高温稳定剂抑制溶剂氧化分解，缓解电芯高温胀气、内阻持续上涨问题；第三安全防护，阻燃添加剂提升电解液闪点，热失控时减缓放热速率，防析钠添加剂抑制负极金属钠析出，从源头杜绝穿刺、短路起火隐患；第四杂质净化，除水、除酸添加剂中和体系微量水分与酸性杂质，避免钠盐水解、电极腐蚀，降低长期静置自放电速率；第五倍率提升，低阻抗界面添加剂减小充放电极化程度，加快钠离子迁移速度，支持 1C 至 3C 大功率快充。各类添加剂协同搭配使用，兼顾储能长循环、动力高倍率、户外极寒场景多重需求，是低成本提升电池产品竞争力的关键手段。

Electrolyte additives have five core optimization functions to comprehensively enhance the electrochemical performance and safety of sodium-ion batteries. First, interface modification: film-forming additives preferentially undergo redox reactions on cathode and anode surfaces to form thin uniform SEI and CEI passivation films, reducing continuous irreversible consumption of electrolytes, slowing capacity fading and effectively extending cycle life. Second, optimization of high and low temperature performance: low-temperature additives reduce overall electrolyte viscosity and freezing point to greatly boost discharge capacity at -20℃, while high-temperature stabilizers restrain solvent oxidative decomposition and alleviate cell swelling and continuous internal resistance rise under high temperatures. Third, safety protection: flame retardant additives raise electrolyte flash points and slow heat release during thermal runaway; sodium precipitation inhibitors suppress metallic sodium deposition on anodes to eliminate fire risks caused by nail penetration and short circuits from the source. Fourth, impurity purification: water and acid scavengers neutralize trace moisture and acidic impurities in the system to prevent sodium salt hydrolysis and electrode corrosion, and reduce self-discharge rate during long-term storage. Fifth, rate capability improvement: low-impedance interface additives mitigate polarization during cycling and accelerate sodium ion migration to support high-rate fast charging from 1C to 3C. Coordinated application of various additives balances multiple demands including long-cycle energy storage, high-power dynamic performance and outdoor extreme low-temperature scenarios, serving as a critical low-cost method to improve product competitiveness of batteries.